projects / thirdparty / u-boot.git / blame
| Commit | Line | Data |
|---|---|---|
| 1ea3fbe3 JW |
1 | ============= |
| 2 | TEE uclass | |
| 3 | ============= | |
| 4 | ||
| 5 | This document describes the TEE uclass in U-Boot | |
| 6 | ||
| 7 | A TEE (Trusted Execution Environment) is a trusted OS running in some | |
| 8 | secure environment, for example, TrustZone on ARM CPUs, or a separate | |
| 9 | secure co-processor etc. A TEE driver handles the details needed to | |
| 10 | communicate with the TEE. | |
| 11 | ||
| 12 | This uclass deals with: | |
| 13 | ||
| 14 | - Registration of TEE drivers | |
| 15 | ||
| 16 | - Managing shared memory between U-Boot and the TEE | |
| 17 | ||
| 18 | - Providing a generic API to the TEE | |
| 19 | ||
| 20 | The TEE interface | |
| 21 | ================= | |
| 22 | ||
| 23 | include/tee.h defines the generic interface to a TEE. | |
| 24 | ||
| 25 | A client finds the TEE device via tee_find_device(). Other important functions | |
| 26 | when interfacing with a TEE are: | |
| 27 | ||
| 28 | - tee_shm_alloc(), tee_shm_register() and tee_shm_free() to manage shared | |
| 29 | memory objects often needed when communicating with the TEE. | |
| 30 | ||
| 31 | - tee_get_version() lets the client know which the capabilities of the TEE | |
| 32 | device. | |
| 33 | ||
| 34 | - tee_open_session() opens a session to a Trusted Application | |
| 35 | ||
| 36 | - tee_invoke_func() invokes a function in a Trusted Application | |
| 37 | ||
| 38 | - tee_close_session() closes a session to a Trusted Application | |
| 39 | ||
| 40 | Much of the communication between clients and the TEE is opaque to the | |
| 41 | driver. The main job for the driver is to receive requests from the | |
| 42 | clients, forward them to the TEE and send back the results. | |
| 43 | ||
| 44 | OP-TEE driver | |
| 45 | ============= | |
| 46 | ||
| 47 | The OP-TEE driver handles OP-TEE [1] based TEEs. Currently it is only the ARM | |
| 48 | TrustZone based OP-TEE solution that is supported. | |
| 49 | ||
| 50 | Lowest level of communication with OP-TEE builds on ARM SMC Calling | |
| 51 | Convention (SMCCC) [2], which is the foundation for OP-TEE's SMC interface | |
| 52 | [3] used internally by the driver. Stacked on top of that is OP-TEE Message | |
| 53 | Protocol [4]. | |
| 54 | ||
| 55 | OP-TEE SMC interface provides the basic functions required by SMCCC and some | |
| 56 | additional functions specific for OP-TEE. The most interesting functions are: | |
| 57 | ||
| 58 | - OPTEE_SMC_FUNCID_CALLS_UID (part of SMCCC) returns the version information | |
| 59 | which is then returned by TEE_IOC_VERSION | |
| 60 | ||
| 61 | - OPTEE_SMC_CALL_GET_OS_UUID returns the particular OP-TEE implementation, used | |
| 62 | to tell, for instance, a TrustZone OP-TEE apart from an OP-TEE running on a | |
| 63 | separate secure co-processor. | |
| 64 | ||
| 65 | - OPTEE_SMC_CALL_WITH_ARG drives the OP-TEE message protocol | |
| 66 | ||
| 67 | - OPTEE_SMC_GET_SHM_CONFIG lets the driver and OP-TEE agree on which memory | |
| 68 | range to used for shared memory between Linux and OP-TEE. | |
| 69 | ||
| 70 | The GlobalPlatform TEE Client API [5] is implemented on top of the generic | |
| 71 | TEE API. | |
| 72 | ||
| 73 | Picture of the relationship between the different components in the | |
| 74 | OP-TEE architecture: | |
| 75 | ||
| 76 | U-Boot Secure world | |
| 77 | ~~~~~~ ~~~~~~~~~~~~ | |
| 78 | +------------+ +-------------+ | |
| 79 | | Client | | Trusted | | |
| 80 | | | | Application | | |
| 81 | +------------+ +-------------+ | |
| 82 | /\ /\ | |
| 83 | || || | |
| 84 | \/ \/ | |
| 85 | +------------+ +-------------+ | |
| 86 | | TEE | | TEE Internal| | |
| 87 | | uclass | | API | | |
| 88 | +------------+ +-------------+ | |
| 89 | | OP-TEE | | OP-TEE | | |
| 90 | | driver | | Trusted OS | | |
| 91 | +------------+-----------+-------------+ | |
| 92 | | OP-TEE MSG | | |
| 93 | | SMCCC (OPTEE_SMC_CALL_*) | | |
| 94 | +--------------------------------------+ | |
| 95 | ||
| 96 | RPC (Remote Procedure Call) are requests from secure world to the driver. | |
| 97 | An RPC is identified by a special range of SMCCC return values from | |
| 98 | OPTEE_SMC_CALL_WITH_ARG. | |
| 99 | ||
| 100 | References | |
| 101 | ========== | |
| 102 | ||
| 103 | [1] https://github.com/OP-TEE/optee_os | |
| 104 | ||
| 105 | [2] http://infocenter.arm.com/help/topic/com.arm.doc.den0028a/index.html | |
| 106 | ||
| 107 | [3] drivers/tee/optee/optee_smc.h | |
| 108 | ||
| 109 | [4] drivers/tee/optee/optee_msg.h | |
| 110 | ||
| 111 | [5] http://www.globalplatform.org/specificationsdevice.asp look for | |
| 112 | "TEE Client API Specification v1.0" and click download. |